folks I want you to rate the MH games by a scale of whether it's worth playing to completion or not.
From most worth it to least worth it:
GU > 3U > 4U > Worldborne/Risebreak > FU > Dos > MH1 > Wilds
GU is self explanatory, it's the most fully packed game in the series with a fun combat system and it's easy to play with friends.
3U (and tri) offer a very unique experience with underwater that is worth experiencing, and the 3rd gen roster introduced a lot of great monsters.
4U is like the middle ground between 3U and GU (both figuratively and literally) in terms of mechanics. Its roster is a bit too bloated with shitty subspecies and the maps can be annoying to play around, but the newcomers in 4th gen are all great. Good for people who want combat that's faster than 3U but less flashy than GU.
The 5th generation games are make or break for some people. I think World handled exploration really well, and Rise's combat and monsters are really fun, at the expense of streamlining exploration and survival elements. Still think they're worth playing, but keep in mind that the experience they offer are both very different from the three games above.
Dos and MH1 were both antiquated games even at the time of release. To shed some perspective, by the time Dos came out, we had action games like DMC3 and God of War. Even if you wanted really slow combat against big baddies, Shadow of the Colossus had already come out by that time. Mechanically the games are more annoying than they are fun or immersive, having every small monster aggro onto you the second you enter an area isn't really that fun or interesting to deal with. Both games have really good atmospheres within the maps, but I wouldn't really recommend playing them to completion beyond that. Arguably the series didn't start to find its footing until Freedom Unite, so I'd say play that instead if you're looking for a super old school experience.
Wilds handles all of the returning elements worse than its contemporaries. Its combat is worse than GU and Rise, it has far worse exploration than World, the unique experience it offers with its story and "seamless" world is shit and far less interesting than underwater, most of the new monsters are shit and don't hold a candle to 3rd or 4th gen monsters, and the atmosphere is worse than MH1/Dos because the maps don't have a color gradient 2/3rds of the time. It is not worth your time and it is definitely not worth your money.